The present invention is directed to motion-base systems for controlling the flow of fluids such as water. It is directed particularly to avoiding flow resulting from erroneous motion or from motion of splashing water.
U.S. Pat. No. 4,520,516 to Parsons describes a flow control system in which flow through a faucet or other conduit is controlled in response to objects in the vicinity of the faucet outlet. The arrangement described in the Parsons patent is particularly suited to kitchen sinks and similar locations since it controls flow in response to the object's motion rather than its mere presence. As a result, a stack of dishes under the faucet does not cause water to flow unless the user moves one of the dishes.
The Parsons arrangement employs ultrasound, transmitting it into the target region and sensing any resultant echo. The time of occurrence of the resulting echo is an indication of the distance to the object that caused it, and differences between successive distance measurements are taken as an indication of object motion.
In short, controlling the valve in response to object motion causes the water to flow in almost all situations in which flow is desired, yet it avoids causing water to flow in many situations in which triggering on simple object presence would cause unintended flow.
However, there still remain certain conditions under which unintended flow occurs even with a motion-based control scheme. In most of these conditions, it is the water itself whose motion causes the unintended flow. For instance, water dripping from the faucet causes splashing at the water surface, and the resultant motion can cause the water to flow. That flow causes more motion, and the water keeps flowing even though it should not.
Another condition is the presence of standing water. Standing water can act as a sonic mirror, reflecting sound substantially in only one direction rather than scattering it in a wide range of directions, as most objects do. Such reflection can occasionally cause standing water to reflect the ultrasound echo away from a sensing transducer. When this happens, the sensor momentarily fails to detect the water surface, which it had been detecting as an object, and instead it detects an object farther away. The system can interpret this change in detected the distance as motion, and unintended water flow can result.